Chapter 31: Images and Optical Instruments

Similar presentations

1 Chapter 31: Images and Optical InstrumentsReflection at a plane surfaceImage formationThe reflected rays entering eyes lookas though they had come from image P’.virtualimagePP’Light rays radiate from a point objectat P in all directions.

3 Reflection and refraction at a plane surfacei (or s’) is the image distances is the object distance:|s| =|i|Image formations’Sign Rules:Sign rule for the object distance:When object is on the same side of the reflectingor refracting surface as the incoming light, the objectdistance s is positive. Otherwise it is negative.(2) Sign rule for the image distance:When image is on the same side of the reflecting orrefracting surface as the outgoing light, the imagedistance i ( or s’) is positive. Otherwise it is negative.(3) Sign rule for the radius of curvature of a sphericalsurface:When the center of curvature C is on the same sideas the outgoing light, the radius of the curvature ispositive. Otherwise it is negative.

4 Reflection at a plane surfaceImage formationimage is erectimage is virtualMultiple image due to multipleReflection by two mirrorshh’m = h’/h=1lateral magnification

5 Reflection at a plane surfaceImage formationWhen a flat mirror is rotated, howmuch is the image rotated?

7 Reflection at a spherical mirrorFocal points at concave and convex mirrorFocal point or focus: Point F at which rays from a source point arebrought together (focused) to form an image.Focal length: Distance f from mirror where focus occurs.f=R/2 where R is the radius of a spherical mirror.

8 Reflection at a spherical mirrorFocal points at a concave mirrorobjecthdimages’If

9 Reflection at a spherical mirrorImage of an extended object at a concave mirrorreal imagePrinciple rays: Light rays that can be traced (more easily) from the sourceto the image:1. Parallel to optical axis2. Passing through the focal point3. Passing through the center of curvature4. Passing through the center of the mirror surface or lens

22 Convex Lens Sign rules for convex and concave lens: Sign Rules:Sign rule for the object distance:When object is on the same side of the reflectingor refracting surface as the incoming light, the objectdistance s is positive. Otherwise it is negative.(2) Sign rule for the image distance:When image is on the same side of the reflecting orrefracting surface as the outgoing light, the imagedistance i (or s’) is positive (real image). Otherwise it is negative(virtual image).(3) Sign rule for the radius of curvature of a sphericalsurface:When the center of curvature C is on the same sideas the outgoing light, the radius of the curvature ispositive. Otherwise it is negative.

36 Microscope small magnifier Object is placed near F1 (s1~f1).q2ismallObject is placednear F1 (s1~f1).Image by lens1is close to thefocal point oflens2 at F2.magnifierimage ang. size

37 Refracting telescope Image by lens1 is at its focal point which isthe focal point of lens 2image distanceafter lens1image height by lens1 at its focal pointmagnifierangular size of image by lens2; eyeis close to eyepiece

42 ExercisesProblem 1What is the size of the smallest vertical plane mirror in which a womanof height h can see her full-length?Solutionxx/2The minimum length of mirror fora woman to see her full height hIs h/2 as shown in the figure right.(h-x)/2h-x

44 Exercises Problem 2 (focal length of a zoom lens) f1 f2=-|f2| f1 r0 I’ray bundlef1r0I’Qr’0r0dxs2d (variable)<f1s’2f(b) Show that the final image I’ is formed a distanceto the right of the diverging lens.

45 Exercises Problem 2 (focal length of a zoom lens) f1 f2=-|f2| f1 r0 I’ray bundlef1r0I’Qr’0r0dxs2d (variable)<f1s’2f(c) If the rays that emerge from the diverging lens and reach the finalimage point are extended backward to the left of the diverging lens,they will eventually expand to the original radius r0 at some point Q.The distance from the final image I’ to the point Q is the effective focallength of the lens combination. Find the effective focal length.